This invention relates to amplifier gain control and, more particularly, to digitally controlled amplifier gain reduction.
A system is disclosed in U.S. Pat. No. 4,016,821, issued on Apr. 12, l977, to the applicant herein, wherein logic is used to select and release stitch information stored in a memory in timed relation with the operation of a sewing machine. Digital information from the memory is converted to positional analog signals which control closed loop servo systems including moving coil linear actuators directly controlling the position of conventional stitch forming instrumentalities of the sewing machine to reproduce a pattern of stitches corresponding to the selected stitch information. According to the system disclosed in the referenced patent, circuitry is provided which permits an operator to alter the stored bight and feed motions. Operator influenced means are effective to signal the logic circuitry to selectively apply a holding signal to an FET switch, maintaining the FET switch in the conductive state. Closing of this FET switch inserts the wiper of a potentionmeter in bypass arrangement in the feedback circuit of an operational amplifier interposed between a digital to analog converter for bight or feed and, respectively, the feed or bight servo system. By changing the magnitude of the resistance in the feedback circuit of the operational amplifier, the gain of the amplifier may be selectively reduced, thereby controlling the signal to the feed or bight linear actuator for selective reduction of stitch length or pattern width, respectively.
While the system described above, as disclosed in the aforereferenced U.S. patent, performs satisfactorily, the disclosed override control is an analog function added to a system which is otherwised digitally controlled. It is therefore an object of the present invention to provide digital override feed and bight controls for a stored pattern sewing machine.